title: Toxic effects of dietary methylmercury on immune system development in nestling American kestrels (Falco sparverius).
abstract: This study evaluated the effects of dietary methylmercury (MeHg) on immune system development in captive-reared nestling American kestrels (Falco sparverius) to determine whether T cell-mediated and antibody-mediated adaptive immunity are targets for MeHg toxicity at environmentally relevant concentrations. Nestlings received various diets, including 0 (control), 0.6, and 3.9 µg/g (dry wt) MeHg for up to 18 d posthatch. Immunotoxicity endpoints included cell-mediated immunity (CMI) using the phytohemagglutinin (PHA) skin-swelling assay and antibody-mediated immune response via the sheep red blood cell (SRBC) hemagglutination assay. T cell- and B cell-dependent histological parameters in the spleen, thymus, and bursa of Fabricius were correlated with the functional assays. For nestlings in the 0.6 and 3.9 µg/g MeHg groups, CMI was suppressed by 73 and 62%, respectively, at 11 d of age. Results of this functional assay were correlated with T cell-dependent components of the spleen and thymus. Dose-dependent lymphoid depletion in spleen tissue directly affected the proliferation of T-lymphocyte populations, insofar as lower stimulation indexes from the PHA assay occurred in nestlings with lower proportions of splenic white pulp and higher THg concentrations. Nestlings in the 3.9 µg/g group also exhibited lymphoid depletion and a lack of macrophage activity in the thymus. Methylmercury did not have a noticeable effect on antibody-mediated immune function or B cell-dependent histological correlates. We conclude that T cell-mediated immunosuppression is the primary target of MeHg toward adaptive immunity in developing kestrels. This study provides evidence that environmentally relevant concentrations of MeHg may compromise immunocompetence in a developing terrestrial predator and raises concern regarding the long-term health effects of kestrels that were exposed to dietary MeHg during early avian development.
authors.affiliation: Cooperative Wildlife Research Laboratory, Southern Illinois University, Carbondale, Illinois, USA. fallacarad@battelle.org
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Fallacara
authors.forename: Richard S
authors.initials: RS
authors.lastname: Halbrook
authors.forename: John B
authors.initials: JB
authors.lastname: French
mesh_terms: D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology; D002060:Bursa of Fabricius / Q000187:drug effects / Q000276:immunology; D004032:Diet; D004785:Environmental Pollutants / Q000378:metabolism / Q000633:toxicity*; D046093:Falconiformes / Q000097:blood / Q000254:growth & development / Q000276:immunology*; D007107:Immune System / Q000187:drug effects* / Q000254:growth & development; D007111:Immunity, Cellular / Q000187:drug effects*; D008297:Male; D008767:Methylmercury Compounds / Q000378:metabolism / Q000633:toxicity*; D013154:Spleen / Q000187:drug effects / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D013950:Thymus Gland / Q000187:drug effects / Q000276:immunology
chemical_list: D004785:Environmental Pollutants; D008767:Methylmercury Compounds